Amplifying system



Aug. 4, 1931. R. A. MILLER AMPLIFYING SYSTEM Flled April 2, 1950 //Vl/E/V7'UH R. A. lM/LLER A DRIVE) Patented Aug. 4, 1931 D sraras PATENT OFFICE A. MILLER, OF PLAINFIELD, HEW JERSEY, ASSIGNOR TO BELL TELEPHONE LABORATORIES, INCORPORATED, OF -NEW YORK, N. Y., A CCRPORATION OF NEW YORK AMPLIFYING SYSTEM Application filed April 2, 1930. SerialNo. 440,887.

This invention relates to wave transmis. sion systems, as for example, electrical wave transmitting and amplifying systems for use I in recording sound on films.

\An object of the invention is eficient control of transmission in such systems. 'Another object isfreduction of crosstalk or other noise or distortion.

In onespecific aspect the invention is a sound recording system comprising two condenser transmitters, individual preliminary vacuumv tube amplifiers fed by the transmitters, a main vacuum tube amplifier fed from the preliminary amplifiers and a recording camera with a light-valve string fed from the main amplifier, the main amplifier being connected to the preliminary amplifiers by shielded cables perhaps a hundred feet long and to the camera by a cable perhaps also a hundred feet long, so that the transmitters and the camera may be remote from the main amplifier. The main amplifier includes two transmission volume control potentiometers individual to the two preliminary amplifiers, for feeding the outputs of the preliminary amplifiers to the input transformer of the main amplifier. To avoid deleteriously affecting the impedance relations in the system, these mixing po 'tentiometers are of the constant impedance type disclosed in D. F. Whiting Patent No.

' 1,778,779, October 21, 1930. However, they are connected in parallel to each other at their output sides, with respect to the primary winding of the input transformer of themain amplifier. The main amplifier also includes two substitute impcdances individualtothe two preliminary amplifiers, for

simulating, theimpedances which they pre liminary amplifiers present to the main amplifier, when the preliminary amplifiers are. disconnected from the main amplifier as described hereinafter. The main amplifier also includes two keys or switches individual to the two transmitting channels comprising the transmitters, the transmitter amplifiers and the mixing potentiometers, for controlling these channels and for controlling the polarization of the transmitters, and for controlling the supply of current to the filament and plate circuits of the vacuum tubes of the preliminary amplifiers. Each key, when in its normal position (i. e., its off position),

transmitting waves to the mixing potentiometer that would constitute crosstalk, interference or noise currents as regards signals transmitted to the main amplifier through the other transmitter channel.

lVhen the key is operated to its on position it first closes circuits for polarizing its transmitter and supplying its transmitter amplifier with filament heating current and steady plate current, thereafter opens the short circuit mentioned above, and finally closes the gap which it had made in the transmitter channel and opens the circuit of the simulating resistance. To avoid deleterious effects which the flow of charging current for the transmitter or the starting or stopping of the flow of steady space current for the amplifier tends to produce on the film record, the short circuit is maintained until the steady space current for the transmitter amplifier has been established and when the key is operated to its of!" position, the short circuit is made again before the circuits for energizing the transmitter and the transmitter amplifier are opened.

When either transmitter channel is to be used without the other, a selecting key or,

interference and crosstalk and to prevent that other channel from unnecessarily shunting away from the input tIZLDSfOIIlZI BX. of the main amplifier the transmission sent from the trasmitter channel to be used. This key, moreover, before effecting this disconnection and short circuiting, eliminates the mixing potentiometer of the transmitter channel that is to be used from that channel, to avoid unnecessary attenuation or transmission loss inthe channel. Any attenuation changes or volume control desired then can be obtained by means of potentiometers' iedby. the input transformer and the vacuum tubes of the main amplifier. The elimination of the potentiometer from 1ts' transmitter channel decreases the 1mpedance which its transmitter channelpic sents to the input transformer oi the main amplifier, (and thereby tends to compensate forincreaseofimpedance presemed to the input winding of the input transformer ot-tlie main-amplifierwhich tends to result from-the disconnection of the other transmitter channel, from the main amplif fier), so that" the impedance from-which tho all 3, light-valve string.

input transformer of the amplifier works ismaintained-oithe same order 0 magnitude; whether one transmitter ampii fier,.only, is connected to the main amplifier, or both transmitter amplifiers are connected to the main amplifier.

Theenergization of the vacuum, tubes the main amplifier is controlled by a single key in that amplifier, which its normai (ifle. oil) position opens'the filament and (Z0 plate circuits of thosetubes and short Other objects, aspects and features of the invention will be apparent from the following-description and claims.

The single figure of the drawing-is a circuit diagranrofa sound recordingsystem having the'teatures mentioned above The systenr comprises two transmitter units 1 and 1, a main amplifier lie-2 l'a recording camera "31 The unit 1 compiises a condenser transmitter iand an individual preliminary amplifier A5 fed by thetransmitter and feeding the main amplifier. unit 1 also comprises a condenser transmitter and an individual preliminary amplifier fed by the transmitter and feeding main amplifier; but the unitl is not show n llltle'ttlll since it maybe like the unit 1. Shieldedcables 6' and 6 of a considerable length, for example. 100 feet, connect units Iandl' respectively to the main am- This short circuiting or the The

plifier; and a cable 7 which may also be 100 feet long, for example, connects the main amplifier to the camera. Thus, the unitsl and l and the camera may be remote from the main amplifier.

The main amplifier includes. two. transmission volnme control potentiometers 8 and 8 individual to the two preliminary amplifiers, for feeding the outputs of the. preliminary amplifiers to theinput transformer?) of =a1nplifiers, for. simulating the impedances which the preliminary amplifiers. PTQSQIltztO- the main amplifier, when the preliminary amplifiers are disconnected from the main. amplifier as described hereinafter; The main amplifier also includes two keyszor. switches 11 and 11' individual to the two transmitting channels comprising the transmitters, the transmitter amplifiers. and the" mixing potentiometers, for controlling these channels and for controlling the polarization'oi the transmitters, and for controlling: the supply of current to the filament. and: plate circuits of the vacuumtubes of the. preliminary amplifiers. Each key,.when.in. its normal position as shown (i. e., its. oil position),"has a contact,'12 or 12 as the case may be, connect a conductor'13 or l3 to ground, to thereby short circuit the output end of the circuit connecting its pre-: liminary, or transmitter amplifier to the; main amplifier, and has a spring,l4 011.4% disconnect; at spring 15 or 15 the conductor.

' 13 or 13 from a conductor 16 or 16: lead f.

ing tirough a contact 17 or 17' of akey-BO to the high potential input lead 1810iv 18" of potentiometer 8 or 8 to thereby open at 1 15 or 15 the path-between the short ciroult.

at 12 or 12 and the, otentiometer: 8or 8f i and has a contact, 19 or19, to'connect'contact i l or 14 to the high potential endi ot' the-resistance 10 or 10 to thereby connect the resistance 10 or 10 across the input side of the potentiometer 8 or 8 as a substitute for the oncratin; out utim Qedance of the i 0 l I I transmitter amplifier. In the caseofjeacn transmitter channel, the short circuit and the "opening of the transmitter channel prevent thecnannel from transmitting waves.

isop'erated to its on position it first closes a'lcontact 20 or 20 for connecting the positive pole of battery 21 to conductor 22 or 22 1501 supplying plate current to its transmitter amplifier and polarizing its transmitter, and closes a contact 23or 23 for connecting the positive pole of battery 2% through rheostat 25 or 25 and conductor 26 'or'26 for supplying the transmitter amplifier with filament heating current, thereafter opens at 12 or 12 the short circuit mentioned above, and finally closes the gap which it has made at 14:, 15 or 1 1, 15 in the transmitter channel and opens at 19 or 19 the circuit of the simulating resistance. To avoid deleterious effects which the flow of charging, current for the transmitter or the starting or stopping of the fiow of steady space current for the amplifier tends to produce on the film record, the short circuit is maintained at 12 or 12 until the steady space current for the transmitter amplifier has been established at 20 or 20 and when the key 11 or 11 is operated to its off position the short circuit is made again at 12 or 12 before the circuits for energizing the transmitter and the transmitter amplifier are opened at 20 or 20.

The on positions of the keys 11 and 11 are looking positions.

When either transmitter channel is to be used without the other, a selecting key or switch 30 in themain amplifier is operated from its normal position, in which it is shown, down or up as indicated by the arrowheads in the drawing. It is operated down, i. e., springs 31 and 32 are moved down, when transmitter unit 1 is to be used without transmitter unit 1, or in other words when use of transmitter unit 1 to be dispensed with for the time being; and

it; is operated up, i. e., springs 31 and 32" are moved up,when transmitter uni;- 1 is to be used without transmitter unit 1. Both the down position and the up position -preferably are locking positions. 1

When keys 11 and 11 are-in their on positions, key 30 in its normal position operative'ly connects both transmitter units 1 and 1" 'to feed 5 their potentiometers 8 and 8 through contacts'17 and 17" as indicated above; and operatively connects the output of potentiometer 8 to the'input transformer 93of the main amplifier by connecting the f high potential output lead 33 0f potentiometer 8 through contacts 34 and 35 in series withcontacts 82 and 36 to the high potential input lead 37 of the'transformer 9; and

, operatively, connects the potentiometer 8' to the transformer 9 by connecting the high potential output lead 33" of potentiometer 8 through contacts 34 and 35 in series with contacts 32 and 36 to the high potential input lead 37 of the transformer 9.

. Thenifkey 30 be moved from its normal position to" its down position, it first closes contact 311cc. contact 35, and next opens contact 17 and separates contacts 34 and 35, and thereafter transfers contact 32 from contact 36 to grounded contact 10. The first operationconnects the high potential output lead 13 of transmitter unit 1 to the high potential input lead 37 of transformer 9, the connection extending from conductor 13 through contacts 15 and 14 of key 11, conductor 16, contacts 31 and 35 of key 30, and contacts 32 and 36 of key 80, to conductor 37. The'second operation opens the high potential input lead of potentiometer 8 at contact 17 and opens the high potential output lead of potentiometer 8 at contacts 34 and 35. Thus, the first and second operation have eliminated the potentiometer 8 from its transmitter channel and operatively connected the transmiter unit 1 to the main amplifier directly instead of through the potentiometer 8. The third operation transfers the high potential output lead 33 of potentiometer 8 from the high potential input lead 37 of transformer 9 to ground, the new connection from the conductor 33 extending still. through contacts 34; and 35 but thence through contacts 32 and 40 to ground. Thus, this third operation has disconnected the transmitter channel including transmitter unit 1 and potentiometer 8 from the main amplifier and short circuited the output end of that channel, which reduces interference and crosstalk and prevents that channel from unnecessarily shunting away from the input transformer 9 of the main amplifier the transmission sent from the transmitter unit 1. The elimination of the potentiometer 8 from its channel, as accomplished by the first and second operations, avoids unnecessary attenuation or transmission loss in the channel. Any attenuation changes or volume control desired then, (i. e., when transmitter unit 1 is not being used), can be obtained by means of potentiometers 45, 46, 4L7 of the main amplifier. The elimination of the potentiometer 8 from its transniitter channel decreases the impedance which its transmitter channel presents to the input transformer 9 of the main amplifier, (and thereby tends to compensate for increase of impedance presented to the primary winding of transformer 9 which tends to result from the disconnection of the other transmitter channel from the main ampliof thesubstitute impedances IO and Then the resistance values of the various Whiting applicationreferred to above, the primary-to-secondary' impedance of the transformer 9 in the transmission frequency the moving photogra range ordinarily being considerablyihigher than the impedance from which this transformer works. 7

Restoring the key to its normal position restores the circuits to the condition inowhich they were before key 30 was operated to its down position, that is, to the condition in "which both transmitter units feed the main amplifier through their IniX- ing potentiometers. In the restoration the order of operation of the contacts of key 30 is the inverseofthe order in whichthey operated when the key was moved from its normal position to its down position.

' The operation of key '30,- when it is thrownfrom its normal position to its up position, to disable the transmitter channel comprising transmitter unit 1 and potentiometer 8 and condition the system for use of only the other transmitter channel, is similar to the above described operation that occurs when the key is thrown from its normal position to its down position, and will be apparent without further description. V

he main amplifier comprises four vacuum tube stages connected in tandem between the input transformer 9 and the output transformer 50. The secondary winding of the transformer feeds the lightvalve string 51 of the camera.

battery 24 through a switch 53. The light controlled by the valve is produced by a lamp 54- which is energized from battery 24 through the switch 53, a rheostat 55 and an amineter 56. The light which the light valve string allows to "pass through the valve produces the desired sound record on V phic-film I57. 7 The first'three stagesof the main amplifier comprisethe heater type (homopotential cathode type) tubes A'-61, A'62 and A+63respectively 'The fourth stage comprises tubes A6% and A,-65 in push-pull relation.

'Conductors 66 and 67 tapped from the Y primary winding of transformer 50 feed aninput transformer 68 of arvolume indicator comprising a rectifierttube R7() and a transmission volume indicating meter .71 connected across a resistance '72 in the plate circuit of the tube. The j volume indicator The:

, traced winding 52 for the string is energized from fheater elements of tubes A 61,

A62 and A.63, and the filamentary" having fluctuations removed by a network consisting of a resistance 74: and a condenser 75; A battery 76 having its positive pole grounded supplies to the grid of tubes A-64 and A65 negative grid biasing potential-from which fluctuations are removed by a'network consisting of a resistance 7 7 and a condenser 78. s

The energization of the plate and fila ment circuits of the tubes in the mainWamplifier is controlled by a single key 80 shown in its normal or off position. When operated to its on position, it first closes, at contacts 81, 82 and 83,'three filament heating circuits traced below, and neat closes a contact 84 in the circuits traced below for supplying space current for the tubes,

and thereafter opens at contact 85 a normally closed short circuitacross the path below which connects the transformer 50, and the light valve string. When key 80 is returned to its ofi' position it re-' establishes the short circuit before opening the plate and filament circuits. As indicated above,; this short circuiting of the light valve string prevents the establishing or the decay of the-dc plate currents of tubes A61, -A-62, A63, A64; and 15-65 from causing disturbing currents in the light-valve strings and consequent distortion in the sound record produced on the film 57. y

The filament heatingcircuit for tubes A6l, A'62 and A63 extends from the positive pole of battery 24 through con ductor 86, contact 81 of key 80, conductor 87. rheostat 88, the filament of tube A 61, the filament of tube A-62, another filament of tube A63, to ground. The filament heating circuit for tube A.-65 extends from,

the positive'pole of the battery 24through the conductor 86, arheostat 89, contact 82 of key 80, a resistance 90, andthe filament of, tube A65, to ground. The filament heating circuit for tubes A64 and, R7O extends from the positive pole'of the battery 24 through the conductor 86, therheostat 89, contact 83 of key 80, the filament of tube R 70, and the filament of tube A64, to ground, a 200 ohm resistance. 91

extend from the positive pole of battery 92 through contact 84 of switch 80. Thence the circuit for tube A61 extends through conductors 94, the resistance arm of a resistance-capacity network 95 for removing current fluctuations, and the primary winding of the plate circuit transformer for tube A61 to the plate ofthe tube. cuit for tube A62 extends from the contact 84 through the conductor 94:, the re sistance arm of a resistance-capacity network 96 similar to network 95, and the primary, winding of the plate circuit transformer for tube lie-62 to the plate of that tube. The circuit for tube A63 extends from the contact 84through the conductor 94 and a resistance 97 to the plate of the tube. A blocking condenser 98 prevents do from passing through the primary winding of the plate circuit transformer for the tube. The circuit for tubes A64l and A65 extends from contact '84 through conductor 99, choke coil 100, conductor 101, and thence through the two halves of the primary winding of transformer 50 to the plates of the tubes. The circuit for tube R extends from contact 84 through the conductor 99,

resistance 72 (and meter 71 in parallel therewith), conductor 102, and choke coil 103 to the plate of the tube. A condenser 104 connected between the plate and the filament of the tube assists in the rectifying action of the circuit of the tube.

A key 105 shown in its normal position controls the circuit from transformer '50 through the light-valve string. This circuit is from the upper terminal of the secondary winding of the transformer through conductor 106, upper right hand contact of key 105, the light-valve string 51, lower right hand contact of key 105, and conductor 107 to the lower end of the transformer winding. As indicated above, the contact 85 of key 80 normally connects conductors 106 and 107 to short circuit the light valve string, but this contact opens the short circuit whenever the main amplifier is in use.

By operation of key 105 to its alternate position, a six ohm resistance 108 for simulating the impedance of the light-valve string can be substituted for the light valve string as the load on the secondary winding of transformer 50. The substitution tests the circuit continuity of the string, since the reading of the volume indicator meter 71 depends upon the load on the amplifier tubes A6l and A65 and should not change when the substitution is made, provided the string is in proper condition.

The primary winding of transformer 50 serves as an autotransformer for matching the primary-to-secondary impedance of the input transformer 68 of the volume indicator circuit to the impedance from which it works.

The cir- What is claimed is:

1. The method of operating a wave transmission system having two sources of waves connected to feed a wave transmission channel, which comprises disconn cting one of said two sources and short-circuiting it and so changing the impedance of said other source as to tend to maintain constant, the impedance from which said channel works.

2. The method of operating a wave transmission system including two wave transmitting channels, a wave receiving channel fed by said transmitting channels, and transmission volume adjusting means in one of said transmitting channels, which comprises eliminating the volume adjusting means from the one transmitting channel and disconnecting the other of the two transmitting channels from the receiving channel.

3. In combination, two wave transmitting channels, a wave receiving channel fed by said transmitting channels in parallel, transmission volume adjusting means in each of said two transmitting channels, and switching means operable selectively to eliminate the volume adjusting means from either of said two transmitting channels, at will, and disconnect the other of said two transmitting channeis from said receiving channel.

4. A main amplifier for amplifying waves from a wave transmitting channel which includes a telephone transmitter remote from said main amplifier, a preliminary amplifier fed by and located at the transmitter and a wave transmission path connectin the preliminary amplifier to said main ainplifier, said main amplifier comprising impedance for simulating the operating impedance with which the preliminary amplifier faces said main amplifier, and switching means operable to first close contacts for connection in energizing circuits of the transmitter and the preliminary amplifier,

thereafter open contacts for connection across the end of the wave transmission path at the main amplifier, subsequently close contacts for connection in series in that wave transmission path, and finally open contacts for connection in series between said first mentioned impedance and said main amplifier.

5. A wave transmission system comprising two transmitting channels, a main vac-. uum tube amplifier fed from said transm1tliminary amplifiers face said main amplifier, two switching means individual to said two transmitting channels for first connecting the simulating impedance for the channel across the channel near the main ampli- V fier, thereafter opening the channel at a point between the preliminary amplifier and the simulating impedance, subsequently short circuiting the channel at a point between the preliminary amplifier and the first mentioned'point, and finally deenergiz ing the transmitters and the preliminary I amplifiers, two potentiometers individual to said two transmitting channels, switching means operable to sequentially eliminate either of said potentiometers from circuit and open the output circuit of' the other,

and switching means operable to sequentially short circuit said light-valve string and deenergize said main amplifier.

6. The'method of operating a vacuum tube amplifier which comprises establishing and stopping the flow of steady plate current for,

the amplifier and maintaining the output side of the amplifier short circuited over a '7 period beginning before the steady plate current has been reduced and terminating after the steady plate tablished. I i

7. A'system comprising a light-Valve having a light-valve string, a vacuum tube for feeding said light-valve string, and switching means operable to sequentially short circuit said light-valve string and deenergize said Vacuum tube.

In witness whereof]: hereunto subscribe my name this 25th day of March, 1930.

ROBERT A. MILLER.

current has been es-v 

